RU2191942C2 - Piezoelectric actuator - Google Patents

Abstract

FIELD: piezoelectric actuators for controlling dispensing valves or valve jets mounted in internal combustion engines of transport vehicles. SUBSTANCE: actuator includes piezoelectric member with laminate structure consisting of alternating layers of piezoelectric, respectively piezoceramic materials with gasket between them made of metallic, respectively electrically conductive layers used as electrodes. Such member, after applying electric pulse load to its electrodes, performs pulsating reciprocation motion for changing distance between its two ends arranged one opposite to another. Actuator also has rigid plates placed on ends of piezoelectric member and tightened one with another by means of tightening members between them at preliminary compression degree of piezoelectric member. Above mentioned plates are mutually tightened at least by means of one springy stirrup embracing from outside (with spacing) plates and piezoelectric member arranged between them. EFFECT: simplified design, enhanced reliability of device. 15 cl, 11 dwg

Description

 The present invention relates to a piezoelectric actuator suitable for controlling distribution valves or valve nozzles mounted on internal combustion engines of a vehicle. Such a piezoelectric drive has a piezoelectric element, primarily in the form of a multilayer structure (laminate), consisting of alternating layers of a piezoelectric, respectively piezoelectric ceramic material with a layer between them of metal, respectively, conductive and serving as electrodes of the layers, this element when applied to its electrodes pulsed electric load makes a similarly pulsating reciprocating movement with a change in the distance between its two position nnym ends against each other, and has disposed at the ends of the piezoelectric element rigid plates, strapped to each other acting between the clamping elements with precompression of the piezoelectric element.

 Piezoelectric actuators can be used in vehicles, for example for controlling valve nozzles of an engine, as well as in a brake system with an anti-lock device and an anti-slip system. The control of valve nozzles using such actuators is described, for example, in GB 1320057 A.

 Such valve nozzles have a spray gun, the opening and closing of which is controlled by a shut-off element made as a pusher. On the plunger from the side of the sprayer there is a working surface to which the pressure of the fuel supplied to the sprayer is applied, while the pressure forces tend to shift the pusher to the opening position of the shut-off member. The pusher with its end made as a plunger, the cross section of which is larger than the area of the specified working surface, protrudes into the distribution chamber. The pressure acting in this chamber tends to move the pusher in the direction of closure of the locking member. The distribution chamber communicates through the inlet throttle with a high-pressure fuel supply line and, as a rule, throttled, respectively connected to the outlet throttle, the outlet valve communicates with the drain fuel pipe, in which only a slight pressure is applied. When the exhaust valve is closed, high pressure prevails in the distribution chamber, under the action of which the pusher moves in the direction of closing the shut-off element, respectively, is kept in the closed position against the action of pressure applied to its working surface facing the sprayer. When the exhaust valve is opened, the pressure in the distribution chamber drops, and the magnitude of such a pressure drop is determined by the dimensions of the inlet throttle and the throttle resistance of the open outlet valve, respectively, of the output throttle associated with it. As a result, the pressure in the distribution chamber when the exhaust valve is open decreases so much that the pusher, under the action of pressure forces applied to its working surface facing the sprayer, moves in the direction of opening of the shut-off member, and is accordingly held in the open position.

 The specified exhaust valve can be controlled using a piezoelectric drive, and in comparison with the magnitude of the stroke of the shut-off element of the atomizer for a piezoelectric drive, a sufficiently small amplitude of the reciprocating motion.

 From the application JP-A 7-226514, a piezoelectric drive is known, the piezoelectric element of which is made in the form of a multilayer structure formed by plates of piezoelectric material stacked in a package, the electrical contact with which is provided at their short ends. To this end, corrugated tapes are provided as electrodes, which are in contact with respective plates. To ensure their reliable contact with the piezoelectric plates, these tapes must be pressed against the ends of these piezoelectric plates with a certain clamping force and therefore are practically not suitable for preliminary compression of the piezoelectric element with high force, which would be sufficient to give the entire piezoelectric drive the necessary vibration resistance in harsh conditions operation of a vehicle.

 In addition, a piezoelectric actuator is known from US Pat. No. 4,460,842, the piezoelectric element of which is enclosed in a metal sleeve having, due to lateral slots, an increased ability to elastically deform. In this case, the pre-compression of the piezoelectric element is provided by the end elements screwed into the sleeve from its ends. However, in a piezoelectric drive of this design, a problem arises related to providing electrical contact between the individual multilayer structures that make up the piezoelectric element and a conductor designed to supply high voltage to the drive. This is due to the fact that such a conductor must be insulated relative to the indicated rotatable end elements through which it passes. Such a design is quite laborious in the manufacture and assembly. In addition to this, in the drive of this design there are also certain problems associated with providing the necessary insulation of the high-voltage conductor.

 Piezoelectric actuators have established themselves as reliable control and drive devices. However, when applying, respectively, when installing piezoelectric drives, it must be taken into account that piezoelectric elements made in the form of laminates using the technology of manufacturing multilayer structures should not work in tension, respectively, they can be subjected to only insignificant such tensile loads. As a result, the design of units with a piezoelectric drive can be significantly complicated.

 Based on the foregoing, the present invention was based on the task of developing a piezoelectric drive that would be devoid of the disadvantages of the known solutions, i.e. would have a simple design, would be inexpensive to manufacture and would have high vibration resistance.

 This problem with respect to the piezoelectric drive of the type indicated at the beginning of the description is solved due to the fact that the rigid plates located at the ends of the piezoelectric element are pulled together by at least one spring clamp, which indentedly surrounds these plates and the piezoelectric element located between them .

 An advantage of the piezoelectric drive proposed in the invention is that the use of spring clamps makes it possible to simplify the manufacture of the piezoelectric drive and at the same time ensure reliable and vibration-resistant fastening of individual layers of the multilayer structure of the piezoelectric element, while the direct contact of the spring clamps with the piezoelectric element is limited only by axial interaction with the above rigid plates, and this piezoelectric element itself with spring clamps and does not touch. At the same time, there is enough free space to accommodate the wiring, which, to ensure the necessary electrical contact with the layers of the piezoelectric material, respectively, with the layers located between them, serving as electrodes, is enough simple to bring to the side of the piezoelectric element.

 The piezoelectric actuators according to the invention also allow tensile loads to be applied to them, since there is provided an elastic fitting of the piezoelectric element, which pulls its ends together to create a preliminary compression in the piezoelectric element.

 The invention is based on the well-known idea of creating elastic pre-compression in a piezoelectric actuator element using located, respectively held on it coupling elements acting against the direction of action of a given tensile stress, and thereby creating a constant compressive load, and the piezoelectric element when pulsating, respectively, variable electric of the fields pushes the said ends apart from each other, creating compressive stress in the piezoelectric m material and elastically stretching the skin, and then again shifts the indicated ends towards each other using the energy stored in the elastic skin, creating compressive stress in the piezoelectric element, while useful work can be performed in both directions of movement, the energy of which is transmitted to the external elements .

 The present invention allows optimal use of the fact that the ends, the distance between which when making the piezoelectric element of the working strokes, to transfer the force to the counter supports, respectively, to the driven elements, must be closed with rigid kinematic coupling elements, respectively, end plates, which structurally can be very simply connected by elastic clamping elements - spring clamps to create a permanent force in the piezoelectric element voltage.

 According to one of the preferred options, there are two separate spring clamps, each of which is made mainly of a C-shape and lap covers with its ends of the plate. In addition, the spring clamp can be made in the form of a ring-closed part.

 The sections of the spring clip or spring clips located on the side of the piezoelectric element preferably have a wave-like shape, respectively one or more corrugations.

 According to another embodiment, the spring clamps are preferably made in the form of tape springs located between the rigid plates, respectively, of tape ties, which can be made of round or flat material. For fastening these belt springs, or belt ties, on the rigid plates themselves, it is preferable to provide side fingers. Further, it is preferable that the belt springs, respectively, tape ties, form a loop covering these fingers. In addition, the tape springs, respectively, the tape ties, can be fixed on the fingers using the ears located on these tape ties. In addition, the tape springs, respectively, the tape ties, it is preferable to perform so that they with one of their end section covered the corresponding finger, and the free end was inserted into the axial slot made on the finger. Tape springs, respectively, tape ties, can have a wavy shape between one fingers and one or more corrugations, respectively.

 In another preferred embodiment, the ribbon coupler, respectively, the spring spring, covers the end face, respectively, the end plate of the piezoelectric element, and with the help of the hanging devices attached to its ends or formed with it in one piece end parts are suspended in a recess, respectively, in the grooves of a rigid plate located on the other end of the piezoelectric element.

 It is preferable to place the piezoelectric element in a spring sleeve tightening two bottom parts located at its ends with the creation of pressure on the ends of the piezoelectric element facing them. Preferably, such a spring sleeve seals tightly around the piezoelectric element, protecting it from dirt and moisture.

The pre-compression created in the piezoelectric element is preferably from 500 to 2000 N / cm ² .

 In addition, the spring clamps are preferably electrically insulated from each other and made in the form of contact leads for electrodes.

 It is advisable to carry out spring clamps with insignificant rigidity in such a way that their tensile forces during the pulsating movements of the piezoelectric element changed only relatively little, while, in particular, the magnitude of the force change should be insignificant in comparison with the developed effective force.

Below the invention is described in more detail on the example of the most preferred variants of its implementation with reference to the accompanying drawings, which show:
figure 1 - the first embodiment of the proposed according to the invention, the drive with a partial section;
in Fig.2 is a section by plane II-II of Fig. 1;
FIG. 3 is a modification of an embodiment corresponding to that shown in FIG. 2 section;
figure 4 is another modified embodiment in section;
5 is an embodiment in which elastic tape ties are provided between the end plates located on the drive;
6 is a view along arrow VI of FIG. 5;
in Fig.7 - various embodiments of elastic tape ties;
on Fig - section of one of the embodiments, in which between the end plates of the drive is an elastic sleeve;
in FIG. 9 is a General view of the valve nozzle;
in FIG. 10 is another cutaway embodiment of a drive;
figure 11 is a preferred embodiment of the fastening of the tape spring, serving as a tight fitting of the piezoelectric element.

 According to figures 1 and 2, the piezoelectric actuator 1 has a piezoelectric element 2, which may consist, for example, of many layers of piezoelectric material, between each of which are conductive layers, which are alternately electrically connected to the electrical terminal 3, respectively, with the electrical terminal 4 due to which the piezoelectric element 2 when connecting the contact terminals 3 and 4 with a source of pulsed electrical voltage or an alternating voltage source not shown Ia is driven in a known manner, making pulsating motion in which the distance between the top and bottom of Fig. 1 the ends of the piezoelectric element 2 varies.

 These ends are closed by rigid plates 5, which in the example of FIG. 1 and 2 have a centrally located end groove 6. The groove 6 of the upper according to FIG. 1 and 2 of the plate 5 is parallel to the groove 6 of the lower plate 5. The grooves 6 are used to place and fasten a spring clamp 7 made in the form of a closed ring, which, by the type of frame, covers the piezoelectric element 2 and the plate 5 and the transverse sections of which are included in the grooves 6. Spring the clamp 7 has elastic sections 7 'that extend laterally of the piezoelectric element 2 and which are pre-stretched and accordingly create preliminary compression in the piezoelectric element 2 between the plates 5. To achieve the specified spring stiffness, the sections 7 'have one or more corrugations, respectively a wavy shape, and the tensile forces acting between the plates 5 tend to straighten the corrugations, respectively, the waves.

 The embodiment of FIG. 3 differs from the above example, in particular in that there are two separate C-shaped spring clamps 8 on the piezoelectric element 2 and that one hole 9 is provided in the end plates 5 on the piezoelectric element 2 into which the bent ends of the spring clamps are inserted 8.

 The difference shown in FIG. 4 variants from the variant of FIG. 1 and 2 also consists in the fact that two spring clamps are provided 10. These spring clamps 10 also have end sections inserted into the grooves 6 of the plates 5, which, however, are hook-shaped, with the hook ends entering the corresponding recess made inside the grooves 6 eleven.

 In all of the above embodiments, the spring clamps 7, 8, respectively 10, can be made of spring steel wire of circular cross section. However, in principle, spring clamps can have a different cross-section, and other elastic materials can be used for their manufacture.

 Since two separate clamps 8, respectively 10, are electrically insulated from each other, these clamps can also be made in the form of electrical contact leads and electrically connected to the corresponding contact pads on the piezoelectric element 2 by crimping, soldering, etc.

 In the embodiment shown in FIGS. 5 and 6, lateral pins 12 are provided on each of the end plates 5, which serve to fasten the tape clamps made in the form of elastic tape ties 13. The latter can be made according to FIG. 6 in the form of a loop covering the fingers 12 of the plates 5, which in the region between the fingers 12 has a wave-like shape, and the tension forces acting between the fingers 12 tend to straighten these waves. In the area of the fingers 12, the tape ties 13 may have a larger width in comparison with the narrower corrugated portions of the tape ties.

 Due to the tensile forces of the tape ties 13 acting between the fingers 12, the piezoelectric element 2 also creates a permanent pre-compression in this case.

 In FIG. 7 shows various modified embodiments of the tape ties 13. According to option A, each tape tie 13 can be provided at its ends with an eyelet 14, which it can be worn on one of the fingers 12. According to options B and C, the fingers 12 can have an axial slot into which the end of the corresponding portion 12 of the end portion of the tape tie 13 is inserted.

 In Example B, the tape tie 13 has an S-shaped portion 13 'in the area of the finger 12, which, due to its shape, has a certain elasticity, i.e., strong tensile forces tend to stretch this portion 13' into a straight line.

 In the exemplary embodiment of Fig. 8, one of the end ends of the piezoelectric element 2 is provided with a plate 15 concave towards the end side, and a plate 16 is provided at its other end, which has an elongated protrusion 17 opposite to the element 2 and made in the form of a pusher. the edge of the plate 16 is surrounded by an annular flange 18 connected to the annular bottom part 19 of the spring sleeve 20, the other end of which is held in the bottom part 21, which with its convex section located on the inside enters the concave section there is a tensile stress on the spring sleeve 20 so that the bottom parts 19 and 21, acting on the piezoelectric element 2, create a corresponding preliminary compression therein.

 The spring sleeve 20 has a generally cylindrical shape in the upper part of FIG. 8, while its lower part is bellows-shaped corrugations, with each of the corrugations preferably forming a semicircular arc, as shown in FIG.

The wall thickness of the sleeve, preferably made of spring steel, can be from 0.1 to 0.6 mm, preferably about 0.3 mm. The maximum tensile stress in the corrugated zone should not exceed 800-900 N / mm ² . Due to the large number of corrugations, the total tensile stress of the spring sleeve 20 can be from about 500 to 1500 N. With a cross-section of the piezoelectric element of the order of 1 cm ^{2, the} pre-compression force can be from about 500 to 2000 N / cm ² .

 On the bottom part 21 there is a carrier plate 22, which in turn is fixed in a cup-shaped cover 23. The bottom part 21, the carrier plate 22 and the cover 23 have mutually coaxial holes through which the terminals 3 and 4 are passed, and the holes made in these holes in the form of plugs, plugs 25, which optionally can be formed by filling the sealing material. On the plugs 25, connecting contacts 26 are provided, through which an electrical voltage can be applied to the piezoelectric element 2.

 The cover 23 is connected to a cylinder 27, which covers with a radial clearance the spring sleeve 20 and the lower end of which is provided with an internal thread that allows, as described below, to screw this cylinder on the valve nozzle body.

 According to FIG. 9, a nozzle 30 controlled by a needle 29 is located on the composite housing 28 of the illustrated valve nozzle assembly, to which fuel can be supplied under high pressure through the hole 31 provided in the housing into which the needle 29 is inserted. The hole 31 in the housing expands upward, passing into a cylindrical working chamber 32 for a pusher 33 rigidly connected to the needle 29 and executed as a plunger, which is located inside the working chamber 32 with the possibility of reciprocating motion. The bottom of FIG. 9, the enlarged end zone of the working chamber 32 is communicated through the invisible in FIG. 9, an opening in the housing with a transverse opening 34, which is connected through a slotted filter 35 to a fuel supply pipe not shown in the drawing. The transverse hole 34 terminates in an annular cavity 36 communicating via an inlet choke 37 with a top in FIG. 9 by the end zone of the working chamber 32. Next, to the upper end zone of the working chamber 32 is adjacent an opening 39 provided with an output choke 38 and located coaxially with the working chamber 32. This opening 39 ends in an adjacent coaxial hole 40 connected to the discharge cavity 41, as well as compensation hole 42, which is parallel to the hole 40 and connects its ends to each other. A distribution valve 43 is installed in the hole 40, which controls the end of the hole 39 facing it and thereby connecting the hole 39 to the discharge cavity 41. The distribution valve 43 is driven by a pusher 44 installed in the hole 40, which in turn is controlled by the piezoelectric actuator 1. This the piezoelectric actuator 1 is installed in the cylinder 27, the inner cavity of which is sealed with a membrane 46 fixed between the adjacent body part 45 and the cylinder 27, preventing ingress into this cavity of fuel.

 Shown in the drawing, the device operates as follows. When an electric alternating voltage or a pulsed electric voltage is applied to the piezoelectric actuator 1, the piezoelectric element 2 begins to make pulsating movements, which are transmitted to the pusher 44 through the elongated protrusion 17 on the piezoelectric element 2, respectively, on the end plate 5 located on it, resulting in the latter opens, respectively closes, the control valve 43. When the control valve 43 is closed, the fuel pressure, supply through the transverse hole 34, acts on both ends of the plunger-type plunger 33. As the cross section of the lower end is reduced by the cross-section of the needle 29 in comparison with the upper end, the pusher 33 is pushed down under the influence of fuel pressure, as a result of which the needle 29 closes sprayer 30. As soon as the control valve 43 opens, the pressure at the upper end of the pusher 33 will begin to drop, and the magnitude of such a pressure drop is determined by the ratio of the resistances of the inlet choke 37 Khodnev throttle 38. As a result, the fuel pressure applied thereby to the lower end of the push rod 33 lifts the plunger 33 and the needle 29 therefore opens sprayer 30.

 Shown in FIG. 10, the embodiment differs from the embodiment of FIG. 8 primarily by the fact that instead of the spring sleeve 20 according to FIG. 8 a wave-shaped belt spring 48 is provided, which covers the opposite side of the annular flange 18 from the piezoelectric element 2 and has a hole in this place for an elongated protrusion 17 of the plate 16.

 Both ends of the tape spring 48 are fixed using high-temperature soldering (soldering with copper solder) in a nipple-shaped suspension device 49 mounted on a disk-shaped support compensator 50, which in turn is adjacent to the end plate 51 of the piezoelectric element 2. In the reference compensator 50, is as in the end plate 51, grooves open to the outside are provided, through which a band spring 48 is passed.

 Instead of suspension devices 49, rigidly connected to the belt spring 48, on the latter according to option A of FIG. 11, the anchor end portions 52 can also be molded in one piece with it. The latter, as shown in FIG. 11 embodiment are made in the form of mainly square legs with a central hole for gripping the tool. In this case, the dimensions of each end part 52, respectively forming its legs, are selected such that this foot overlaps in the transverse direction the groove, which is located in the end plate 51, respectively, in contact with the supporting compensator 50, and through which the belt spring 48 is passed, and relies on the corner sections 52 'on both sides of the specified groove on the end side of the support compensator 50 or end plate 51.

 The transitions between the corner sections 52 'and the relatively narrow part of the tape spring 48 passed through the slot are made in the form of a recess in the U-shape or preferably in the form of a keyhole so that the corner sections 52' form short tabs on the end portion 52, directed towards face of the supporting compensator 50, respectively, of the end plate 51, and this shape prevents the formation of cracks in the transitions.

 According to embodiment B of FIG. 11, which shows a first embodiment of the end portion 52 in a side view along arrow P shown in embodiment A of FIG. 11, the corner portions 52 'can be made substantially flat and lie approximately in the same plane as the rest of the end portion 52 .

 Instead, in another example, which is preferred, the ends of the corner portions 52 'according to embodiment B of FIG. 11 can also be bent relative to the plane of the end portion 52 so that each of the bent parts of the corner portion 52' is supported by a plane facing the end side of the reference compensator 50.

Claims (15)

 1. A piezoelectric actuator suitable for controlling distribution valves or valve nozzles mounted on internal combustion engines of a vehicle, having a piezoelectric element (2), primarily in the form of a multilayer structure consisting of alternating layers of piezoelectric or piezoelectric ceramic material with a layer between them of metal, respectively conductive, and serving as the electrodes of the layers, and this element is applied to its electrodes imp A full electric load makes a similarly pulsating reciprocating movement with a change in the distance between its two opposite ends, as well as having rigid plates (5, 15, 16) located at the ends of the piezoelectric element (2), pulled together with each other acting between them clamping elements (7, 8, 10, 13, 20) with preliminary compression of the piezoelectric element (2), characterized in that said plates (5) are pulled together by at least one spring clamp (7, 8, 10), which s from blunt covers respectively surrounds the outside of the plate and a piezoelectric element located between them (2).  2. The drive according to claim 1, characterized in that there are two separate spring clamps (8, 10), each of which is made mainly of a C-shape and lap covers the ends of the plate (5).  3. The drive according to claim 1, characterized in that the spring clamp (7) is made in the form of a part closed by the type of ring.  4. The drive according to any one of claims 1 to 3, characterized in that the sections of the spring clamp, respectively of the spring clamps (7,8,10), located on the side of the piezoelectric element (2), have a wave-like shape, respectively one or more corrugations.  5. The drive according to claim 1, characterized in that the spring clamps are made in the form of tape springs, respectively, tape ties (13) located between the rigid plates.  6. The drive according to claim 5, characterized in that on the plates (5) there are lateral fingers (12) for fastening the belt springs, respectively, of the tape couplers (13).  7. The drive according to claim 6, characterized in that the tape springs, respectively, tape ties (13), form a loop covering the fingers (12).  8. The drive according to claim 6, characterized in that the tape springs, respectively, the tape ties (13), are mounted on the fingers (12) using the ears located on the tape couplers (14).  9. The drive according to claim 6, characterized in that the belt springs, respectively, the tape couplers (13), with one of their end sections cover the corresponding finger (12) and are inserted with the free end into the axial slot made on the finger.  10. A drive according to any one of claims 6 to 9, characterized in that the tape springs, respectively, the tape ties (13), have a wavy shape, respectively one or more corrugations, in the area between the fingers (12).  11. The drive according to claim 1 or 5, characterized in that the tape coupler, respectively, the tape spring (48), covers the end face, respectively, the end plate (16, 18), the piezoelectric element (2) and with the help of hanging devices attached to its ends (49) or the end parts (52) formed with it in one piece, suspended in a recess, respectively, in the slots of the plate (51) located on the other end of the piezoelectric element (2).  12. The drive according to claim 1, characterized in that the piezoelectric element (2) is located in the spring sleeve (20), tightening the two bottom parts located at its ends (19, 21) with the creation of pressure on the ends of the piezoelectric element facing them (2) )  13. The drive according to claim 12, characterized in that the spring sleeve (20) hermetically covers the piezoelectric element (2), protecting it from dirt and moisture. 14. The drive according to any one of claims 1 to 13, characterized in that the preliminary compression created in the piezoelectric element (2) is 500-2000 N / cm ² .  15. The drive according to claim 2, characterized in that the spring clamps (8, 10) are electrically insulated from each other and are made in the form of contact leads for electrodes.

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